This is a four-year, longitudinal, developmentally oriented nosologic study of childhood depression with youngsters aged 8-13 years. A structured clinical interview is used to facilitate reliable psychiatric assessment. It is posited that the child's stage of cognitve development will mediate the clinical expression of the disorder. A three-index measure of cognitive development has been devised (a Piagetian task and two tasks of social, intra- and interpersonal cognition). Stage of pubertal development is also determined. It is hypothesized that a developmental framework may clarify the confusing phenomenological picture of childhood depression which currently dominates the literature. A longitudinal sequential design is used to validate the concept of childhood depression and the developmentally oriented nosology. A depressed cohort of 120 children will be selected based on symptom criteria derived from the literature on which there was high "expert agreement." They are obtained from Pittsburgh Child Guidance and from an out-patient service of children's Hospital of Pittsburgh. The subjects are re-evaluated at 2- 6- 12- 18- and 24-months after study entry. They will be contrasted with an equated sibling comparison group of 50 nondepressed subjects reassessed at 12- and 24-months. The repeated assessment of the child through clinical, self- and parental ratings and pediatric evaluation, the evaluation of parental psychiatric status through clinical- and self-ratings and determination of familial psychiatric history will facilitate a detailed characterization of the cohorts. The study will contribute to a developmentally oriented nosology of childhood depressive disorders and may provide some evidence as to appropriate treatment approaches.